1. Field of the Invention
This invention relates to arc detection in alternating current (AC) power systems.
2. Description of the Related Art
Electrical power systems often distribute power as an alternating current (AC) waveform, both for historical and engineering reasons. Although the standard 60 Hz frequency is commonly used by power utilities, other frequencies such as 400 Hz are also used, for example, in civilian and military aircraft.
Any electrical power system can be troubled by undesired electrical arcing, which can cause power failure, equipment destruction, and which in severe cases can even lead to fire or explosion. The problems of electrical arcing are particularly critical in aircraft, ships, around flammable fluids or in other environments in which human life depends on proper electrical functions. In these and other applications the reliable and early detection of electrical arcs is crucial.
Previous approaches to arc detection in AC power systems include monitoring the power waveform for wideband high frequency noise and examining the detected noise to find patterns of variation synchronized to the power waveform. See for example, U.S. Pat. No. 5,729,145 to Blades (1998); Blades includes a survey of prior art arc detection patents. High frequency noise monitoring methods do not allow the monitoring system to respond to frequency components of the arc signature, which may lie in the general frequency range of the AC fundamental. Furthermore, false alarms are not precluded by such methods, which still respond to harmonics of the AC fundamental, whether or not arc related.
Some previous methods (including that of the Blades U.S. Pat. No. 5,729,145) require that the spectrum of the arc signature be correlated to line frequency fundamentals. Such methods do not adequately detect more chaotic arc signatures, and they are plagued by false alarms related to transient load conditions, which are often well correlated to line frequencies.
An effective electric arc monitoring system should not only detect arc conditions, but should discriminate true arc signatures from power supply transients or other conditions that are not arc related. False alarms should be eliminated or limited to the greatest possible extent.